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Unformatted text preview: 1 Announcements HW #2 is Due on Thursday (September 8) as usual. Ken will be in RH111 so please visit with him. Exam #1 is on Tuesday (September 13) We will have a short (30 min) review on Monday, Sept 12. at 3:25 pm in RH103 Radiation travels as waves . Waves carry information and energy. Review: Properties of a wave wavelength ( ) crest amplitude (A) velocity (v) trough is a distance, so its units are m, cm, or mm, etc. Period (T): time between crest (or trough) passages Frequency ( ): rate of passage of crests (or troughs), = EM waves: c = 1 T (units: Hertz or cycles/sec) cold dust hotter star (Sun) cool star frequency increases, wavelength decreases Approximate black-body spectra of astronomical objects demonstrate Wiens Law and Stefans Law very hot stars Example: Blackbody - the microwave background Clicker Question: Compared to sound waves, radio waves travel: A: faster B: slower C: at the same speed Clicker Question: Compared to visible light, X-rays travel: A: faster B: slower C: at the same speed 2 Clicker Question: Electromagnetic radiation penetrates the Earths atmosphere at what wavelengths?: A: at visible, ultraviolet, and gamma-ray wavelengths B: at all wavelengths C: only at infrared wavelengths D: only at optical wavelengths E: at radio, visible, and part of the infrared wavelengths c = 1 nm = 10-9 m , 1 Angstrom = 10-10 m The Electromagnetic Spectrum Spectroscopy and Atoms How do you make a spectrum? For light, separate white light into its colors using a glass prism or "diffraction grating". For radiation in general, spread out the radiation by wavelength (e.g car radio, satellite TV receiver). How we know these things: - Physical states of stars, gas clouds, e.g. temperature, density, pressure. - Chemical make-up of stars, galaxies, gas clouds - Ages of stars and galaxies - Masses of stars, clouds, galaxies, extrasolar planets, rotation of galaxies, expansion of universe, acceleration of universe....
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- Fall '09